THE NATIONAL GEOGRAPHIC MAGAZINE
Photograph by W. D. Staats
CENSUS TAKERS COUNT FISH AS THEY REACH THE TOP OF THE "WATER STAIRS"
A submerged white platform shows up weary salmon as they cross the upper "landing" of a
Bonneville Dam fishway. During the first six months' actual count, almost half a million salmon
and steelhead trout passed the dam on the way up the Columbia River (pages 187 and 190).
gration is probably longer than that of any
other species of salmon or trout. The pink
salmon (Plate X) migrates least of all Pa
cific salmon; it spawns only a few miles
above salt water.
In trout, Salmo, and charrs, Salvelinus,
the migratory instinct is definitely devel
oped, but these forms pass most or all of
their lives in fresh water, and thus there
is no necessity for their migrating so far.
The salmon, in their urge to reach the
proper place to deposit their eggs, often wear
themselves out trying to navigate water
falls or fish ladders placed in dams. Pacific
salmon will jump vertically four times their
length or more (page 190).
Sometimes they are killed by falling
backward and striking sharp rocks. If not
seriously injured, they continue to leap
until they either go over the obstruction or
drift exhausted downstream to fall prey to
birds, bears, or other predators. By the
time they have spawned, both salmon and
trout are weakened and often emaciated.
This worn-out condition is not, however,
the chief cause of the death after spawn
ing of the five species of Pacific salmon.
They have reached the end of their life
cycle, and even fish in good condition die
soon after their reproductive period is com
pleted. Trout, steelhead, and charrs may
spawn for several successive years.
One remarkable trait of salmon is their
"homing instinct," their mysterious ability
to return to the stream in which they de
veloped as fry and fingerlings. When eggs
have been taken from females in one river
and transferred to another stream for de
velopment, the young produced have gone
through their life cycle and returned to
spawn in the waters where they were
hatched rather than in the habitat of their
parents. Returning of tagged or marked
fish and study of their scales have proved
that most salmon return to their "home
stream."
LIVE FISH RELATED TO FOSSILS
The Alaskan blackfish, a close relative of
the Washington mud minnow (page 189),
lives in the coastal tundra regions of Alaska
in ponds and streams. It is barely distin
guishable from a similar form living across
the Bering Sea in Asia.
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